Get ready, Fools; we're headed toward a battle royal of epic proportions. Boehringer Ingelheim's Pradaxa was recently approved to treat patients with an erratic heartbeat, and Bayer and Johnson & Johnson (NYSE: JNJ) have a second compound, Xarelto, that isn't far behind.

Data presented at the American Heart Association showed Xarelto lowered the incidence of stroke or a blood clot to just 1.7%, compared with 2.2% of patients taking the current standard of care, warfarin. When you add in the patients that dropped out of the study, the results weren't as impressive: 2.1% for those on Xarelto versus 2.4% for those on warfarin.

But even if Xarelto is only viewed as being as good as warfarin, that should be enough to capture much of the market. Warfarin is a notoriously difficult drug to find the optimal dose for, and it interacts with other foods and medications that patients take.

Is Xarelto better than Pradaxa? It's a little hard to know. Since the inclusion criteria for participating in the trial are a little different, comparing the results between trials is difficult. Until someone does a head-to-head trial comparing the two, we won't know for sure.

But it may not matter much. There's plenty of room for multiple players. This is a multibillion-dollar market after all. Take a look at the anti-inflammatory drugs as a model of how the heart drugs might be able to play well together: There are three drugs that all register sales north of $4 billion in sales annually.

Boehringer Ingelheim, Bayer, and Johnson & Johnson had better hope so. There are multiple companies looking to enter the market behind the two leaders. Pfizer (NYSE: PFE) and Bristol-Myers Squibb (NYSE: BMY) are next with data due out next year for their competing drug, apixaban. Merck (NYSE: MRK) and Japan's Daiichi-Sankyo each have a drug that's farther back.

With very few untapped mega markets left and plenty of blockbusters going off patent, this is one area investors should keep their eye on.

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Pfizer is a Motley Fool Inside Value selection. Motley Fool Options has recommended a diagonal call position on Johnson & Johnson, which is a Motley Fool Income Investor selection. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors.

Fool contributor Brian Orelli, Ph.D., doesn't own shares of any company mentioned in this article. The Fool owns shares of Johnson & Johnson and has a disclosure policy.